nic_uio: probe and attach devices after unload

Added code that saves the pointers to the detached devices, during
driver loading, and during driver unloading, go over the list,
and re-attach them by calling device_probe_and_attach
on each device.

Signed-off-by: Raz Amir <razamir22@gmail.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>